A variety of optical communications modules exist for transmitting and/or receiving optical data signals over optical waveguides, which are typically optical fibers. Optical communications modules include optical receiver modules, optical transmitter modules and optical transceiver modules. Optical receiver modules have one or more receive channels for receiving one or more optical data signals over one or more respective optical fibers. Optical transmitter modules have one or more transmit channels for transmitting one or more optical data signals over one or more respective optical fibers. Optical transceiver modules have one or more transmit channels and one or more receive channels for transmitting and receiving respective optical transmit and receive data signals over respective transmit and receive optical fibers. Bi-directional optical transceiver modules are configured to both transmit and receive optical data signals that are at different wavelengths over each optical fiber. In a bi-directional optical transceiver module, wavelength division multiplexing and demultiplexing techniques are used to multiplex and demultiplex the transmit and receive optical data signals, respectively.
For each of these different types of optical communications modules, a variety of designs and configurations exist. A typical layout of an optical communications module includes a module circuit board, such as a printed circuit board (PCB), a connector, such as an edge connector or a ball grid array (BGA), or the like, and various electrical components, optical components, and optoelectronic components mounted on the module circuit board. In the case of a typical optical transmitter module, one or more light sources such as laser diodes or light-emitting diodes (LEDs) and one or more driver integrated circuits (ICs) are mounted on the module circuit board and electrically interconnected with it. In the case of a typical optical receiver module, the module circuit board has one or more light detectors and a receiver IC mounted on it. Optical transceiver modules typically have one or more light sources, one or more light detectors, a light source driver IC, and receiver IC mounted on the module circuit board.
A typical optical communications module includes a lens block, sometimes referred to as an optical subassembly (OSA), that couples light between the light source or light detector and the end of the optical fiber. The end of the optical fiber is typically held in an optical connector module that mates with a receptacle of the optical communications module. The lens block is precisely located and oriented inside of the housing of the optical communications module and has one or more optical elements (e.g., lenses, reflectors, etc.) that are precisely aligned along the optical pathway(s) of the lens block for operating on the optical signals being coupled by the lens block between the light detector or light source and the end of the optical fiber. The optical elements of the lens block perform various operations including, for example, folding the optical pathway(s), collimating the light beams and focusing the light beams.
Features such as fiducials on the optical communications module housing or on other components of the optical communications module are often used to aid in the mounting of the lens block at a predesignated, aligned position inside of, or on the module housing. Passive and active alignment processes are often used to ensure that the lens block is mounted in its predesignated, aligned position. While such processes are capable of achieving precise positioning and alignment of the lens block relative to other components that are external to the lens block, they often cannot be used to align the optical elements within the lens block. The alignment of optical elements within the lens block is typically the responsibility of the lens block manufacturer. The lens blocks are often made of a molded plastic material. The lens block manufacturer typically checks the alignment of the optical elements by verifying that the mold is properly configured and by verifying that sample lens blocks made using the mold are satisfactory.
However, when the optical elements of the lens block become complicated, or complex, verifying proper alignment of the optical elements within the lens block is difficult. For example, if the lens block includes biconic lens surfaces or even more complicated lens surfaces, verifying proper alignment of the lens surfaces within the lens block is extremely difficult. In most cases, there is no direct way of verifying or measuring alignment. In such cases, the manufacturer often relies on functional optical testing to assess the alignment of the complicated lens surfaces. Functional optical testing judges the optical elements by how well the lens block as a whole performs.
One problem with functional optical testing is that the lens block manufacturers are usually precision mechanical experts, but have no or limited expertise in optics. Therefore, it is unlikely that the manufacturer will have access to or be trained to properly use a functional optical measurement system. Another problem with functional optical testing is that the functional optical measurements are often affected by properties and dimensions of surfaces or elements other than the optical surface or element in question. Consequently, it is very difficult to measure or verify proper alignment of individual optical surfaces of the lens block. Relying only on the functional optical measurement of the entire lens block usually results in the lens block having nominal performance that is not as good as the lens block design and much narrower tolerance windows than those of the lens block design. For these reasons, the inability to measure and correct each optical surface of the lens block is a limiting factor in making most complex lens blocks today.
Accordingly, a need exists for a way to measure alignment of complex optical surfaces of a lens block. A need also exists for a way to determine a correction that needs to be made to the manufacturing process to correct a misaligned complex optical surface of a lens blocks.